Envelope For Lighter-Than-Air Aircraft

ABSTRACT

An envelope is disclosed for holding gas in a lighter-than-air aircraft. The envelope includes a shell having upper and lower hemispheres. The upper hemisphere has the shape of a hemisphere of a generally oblate spheroid defined by equatorial radii and a polar radius. The lower hemisphere has the shape of a hemisphere of a generally oblate spheroid defined by equatorial radii and a polar radius. The lower hemisphere is inverted compared to the upper hemisphere. The equatorial radii of the upper hemisphere are equal to the equatorial radii of the lower hemisphere. The upper hemisphere is joined with the lower hemisphere at their respective equators. The volume of the upper hemisphere is greater than the volume of the lower hemisphere. The height of the shell is less than the diameter of the shell at the joined equators.

BACKGROUND OF THE INVENTION

Lighter-than-air aircraft take many forms and have a variety of uses. Primary uses for unmanned high altitude lighter-than-air aircraft are for surveillance and communications. Often, it is desirable that these aircraft maintain their position, or station keep.

Traditionally, these high altitude aircraft fly below 70,000 feet. It would be greatly advantageous to fly above 70,000 feet to be above atmospheric turbulence and disruptive weather, and to deconflict from commercial, private, and military fixed wing aircraft. However, at altitudes above 70,000 feet, strong winds are present. In order to station keep in these strong winds, it is highly useful for the aircraft to have a low aerodynamic drag.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of the envelope of the present invention.

FIG. 2 is a side elevation of the envelope of the present invention.

FIG. 3 is a top elevation of the envelope of the present invention.

FIG. 4 is a front elevation of the envelope of the present invention.

FIG. 5 is an exploded view of the side elevation of FIG. 2.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1-4 illustrates envelope 2 for holding gas in a lighter-than-air aircraft. Envelope 2 includes a shell 4. Shell 4 has an upper hemisphere 6 and a lower hemisphere 8 divided by equator 10.

Upper hemisphere 6 has the shape of a hemisphere of a generally oblate spheroid defined by equatorial radii 12, 14 and polar radius 16. In an oblate spheroid, polar radius 16 is less than equatorial radii 12, 14 and equatorial radii 12, 14 are equal to one another. Upper hemisphere 6 may be truly oblate, or may deviate from truly oblate. In one embodiment, upper hemisphere 6 deviates from truly oblate with one equatorial radius 12 being longer than the other equatorial radius 14. In one embodiment, the ratio of the smaller equatorial radius 14 to the larger equatorial radius 12 is between 0.75 and 1. For example, the ratio of the smaller equatorial radius 14 to the larger equatorial radius 12 may be 0.9. In the context of the present invention, a ratio in the range of between 0.75 and 1 is defined to be about equal.

In another embodiment, upper hemisphere 6 deviates from truly oblate by extending beyond the boundaries of a perfect oblate spheroid hemisphere, as best seen in FIGS. 3 and 4. The dashed lines represent the boundaries of a generally oblate spheroid with one equatorial radius 12 longer than the other equatorial radius 14. It can be seen that, although the boundaries of shell 4 do not exactly match the boundaries of the oblate spheroid, the boundaries are substantially close.

Lower hemisphere 8 has the shape of a hemisphere of a generally oblate spheroid defined by equatorial radii 18, 20 and polar radius 22. Similar to upper hemisphere 6, lower hemisphere 8 is generally oblate and may not be exactly oblate. Additionally, equatorial radii 12, 14 of upper hemisphere 6 are equal to the equatorial radii 18, 20 of lower hemisphere 8. Lower hemisphere 8 is inverted compared to upper hemisphere 6 and is joined with upper hemisphere 6 at their respective equators 10.

The volume of one hemisphere of an oblate spheroid may be represented by the equation V=4/6 πabc, where a, b, and c are the equatorial radii and the polar radius. In the present invention, the volume of upper hemisphere 6 is greater than the volume of lower hemisphere 8. In one embodiment, the ratio of the volume of upper hemisphere 6 to the volume of lower hemisphere 8 is between 1.2 and 4. For example, the ratio of the volume of upper hemisphere 6 to the volume of lower hemisphere 8 may be 2.3.

The diameter of shell 4 may be represented by doubling an equatorial radius 12, 14, 18, 20. The height of shell 4 may be represented by adding the polar radius 16 of upper hemisphere 6 with the polar radius of lower hemisphere 8. In one embodiment, the height of shell 4 is less than the diameter of shell 4 at the joined equators 10. In one embodiment, the ratio of the diameter of shell 4 to the height of shell 4 is between 2.5 and 5. For example, the ratio of the diameter of shell 4 to the height of shell 4 may be 3.3.

Furthermore, an angle of shell 4 may be calculated from equatorial radii 12, 14, 18, 20 and polar radii 16, 22. The angle of the upper hemisphere is equal to the inverse tangent of polar radius 16 divided by one of the equatorial radii 12, 14. Similarly, the angle of the lower hemisphere is equal to the inverse tangent of polar radius 22 divided by one of the equatorial radii 18, 20. Adding the angles of the upper and lower hemispheres together, yields the angle of shell 4. In one embodiment, the angle of shell 4 is less than or equal to 40 degrees.

Since upper 6 and lower 8 hemispheres are shaped as generally oblate spheroids, envelope 2 may be alternatively described with reference to a cross section of shell 4 traversing the upper and lower hemispheres. In this description, the cross section includes two ellipse halves joined at their major axes. FIG. 5 best illustrates this description. One half of an ellipse 24 defines the shape of upper hemisphere 6. One half of another ellipse 26 defines the shape of lower hemisphere 8. Each of these half ellipses 24, 26 is divided along its major axis 28, 30. The major axes 28, 30 of the ellipses 24, 26 are equal, the semi-minor axes 32, 34 of the ellipses are unequal, and the ellipse 24, 26 halves are joined at their major axes 28, 30.

Since upper 6 and lower 8 hemispheres are shaped as generally oblate spheroids and the equatorial radii 12, 14 are equal to equatorial radii 18, 20, the ratio of the volume of upper hemisphere 6 to the volume of lower hemisphere 8 is directly related to the ratio of the semi-minor axis of upper hemisphere 6 to the semi-minor axis of lower hemisphere 8. Therefore, in one embodiment the semi-minor axis of the upper hemisphere is greater than the semi-minor axis of the lower hemisphere and the ratio of the semi-minor axis of the upper hemisphere to the semi-minor axis of the lower hemisphere is between 1.2 and 4. For example, the ratio of the semi-minor axis of upper hemisphere 6 to the semi-minor axis of lower hemisphere 8 may be 2.3.

In a further embodiment, the semi-major axes, one half of the major axes 28, 30, are greater than the sum of the semi-minor axes 32, 34. In one embodiment, the ratio of the semi-major axes to the sum of the semi-minor axes is between 2.5 and 5. For example, the ratio of the semi-major axes to the sum of the semi-minor axes may be 3.3.

Shell 4 may be further defined with reference to a cross section through the equator of shell 4. This cross section is generally elliptical. In one embodiment, the generally elliptical cross section is defined by a major axis and a minor axis and the ratio of the minor axis to the major axis is between 0.75 and 1. For example, the ratio of the minor axis to the major axis may be 0.9.

The present invention is greatly advantageous over previous high altitude envelope solutions as it reduces drag, enabling a lighter-than-air aircraft using this envelope to maintain its position for a longer period of time, maneuver better, and transit longer distances than has been possible with other envelope designs.

The foregoing description is only illustrative of the invention. Various alternatives, modifications, and variances can be devised by those skilled in the art without departing from the invention. Accordingly, the present invention embraces all such alternatives, modifications, and variances that fall within the scope of the described invention. 

1. An envelope for holding gas in a lighter-than-air aircraft, the envelope comprising: a shell including an upper hemisphere having the shape of a hemisphere of a first generally oblate spheroid defined by first and second equatorial radii and a polar radius and a lower hemisphere having the shape of a hemisphere of a second generally oblate spheroid defined by first and second equatorial radii and a polar radius, wherein the lower hemisphere is inverted compared to the upper hemisphere, the equatorial radii of the upper hemisphere are equal to the equatorial radii of the lower hemisphere, and the upper hemisphere is joined with the lower hemisphere at their respective equators, wherein the volume of the upper hemisphere is greater than the volume of the lower hemisphere, and wherein the height of the shell is less than the diameter of the shell at the joined equators.
 2. The envelope of claim 1 wherein the polar radius of the first generally oblate spheroid is less than the equatorial radii of the first generally oblate spheroid and the polar radius of the second generally oblate spheroid is less than the equatorial radii of the second generally oblate spheroid.
 3. The envelope of claim 1 wherein the first and second equatorial radii of the first generally oblate spheroid are about equal and the first and second equatorial radii of the second generally oblate spheroid are about equal.
 4. The envelope of claim 3 wherein the ratio of the smaller of the first and second equatorial radii of the first generally oblate spheroid to the larger of the first and second equatorial radii of the first generally oblate spheroid is between 0.75 and
 1. 5. The envelope of claim 7 wherein the ratio of the smaller of the first and second equatorial radii of the second generally oblate spheroid to the larger of the first and second equatorial radii of the second generally oblate spheroid is between 0.75 and
 1. 6. The envelope of claim 1 wherein the ratio of the volume of the upper hemisphere to the volume of the lower hemisphere is between 1.2 and
 4. 7. The envelope of claim 1 wherein the ratio of the diameter of the shell to the height of the shell is between 2.5 and
 5. 8. The envelope of claim 1 wherein the angle of the shell is less than or equal to 40 degrees.
 9. An envelope for holding gas in a lighter-than-air aircraft, the envelope comprising: a shell generally including an upper hemisphere having the shape of a hemisphere of an ellipsoid defined by first and second equatorial radii and a polar radius, wherein the first and second equatorial radii are about equal and the polar radius is less than the first and second equatorial radii and a lower hemisphere having the shape of a hemisphere of an ellipsoid defined by first and second equatorial radii and a polar radius, wherein the first and second equatorial radii are about equal and the polar radius is less than the first and second equatorial radii and less than the polar radius of the upper hemisphere.
 10. The envelope of claim 9 wherein the ratio of the smaller of the first and second equatorial radii of the upper hemisphere to the larger of the first and second equatorial radii of the upper hemisphere is between 0.75 and
 1. 11. The envelope of claim 9 wherein the ratio of the smaller of the first and second equatorial radii of the lower hemisphere to the larger of the first and second equatorial radii of the lower hemisphere is between 0.75 and
 1. 12. The envelope of claim 9 wherein the ratio of the volume of the upper hemisphere to the volume of the lower hemisphere is between 1.2 and
 4. 13. The envelope of claim 9 wherein the ratio of the diameter of the shell to the height of the shell is between 2.5 and
 5. 14. The envelope of claim 9 wherein the angle of the shell is less than or equal to 40 degrees.
 15. An envelope for holding gas in a lighter-than-air aircraft, the envelope comprising: a generally oblate spheroid shaped shell having upper and lower hemispheres wherein at least one cross section of the shell traversing the upper and lower hemispheres includes a half of a first ellipse divided along its major axis, defining the shape of the upper hemisphere, and a half of a second ellipse divided along its major axis, defining the shape of the lower hemisphere, wherein the major axes of the ellipses are equal, the semi-minor axes of the ellipses are unequal, and the ellipse halves are joined at their major axes.
 16. The envelope of claim 15 wherein the volume of the upper hemisphere is greater than the volume of the lower hemisphere.
 17. The envelope of claim 17 wherein the ratio of the volume of the upper hemisphere to the volume of the lower hemisphere is between 1.2 and
 4. 18. The envelope of claim 15 wherein the semi-minor axis of the upper hemisphere is greater than the semi-minor axis of the lower hemisphere.
 19. The envelope of claim 17 wherein the ratio of the semi-minor axis of the upper hemisphere to the semi-minor axis of the lower hemisphere is between 1.2 and
 4. 20. The envelope of claim 15 wherein the semi-major axes are greater than the sum of the semi-minor axes.
 21. The envelope of claim 20 wherein the ratio of the semi-major axes to the sum of the semi-minor axes is between 2.5 and
 5. 22. The envelope of claim 15 wherein a cross section through the equator of the shell is generally elliptical.
 23. The envelope of claim 22 wherein the shape of the generally elliptical cross section is defined by a major axis and a minor axis and the ratio of the minor axis to the major axis is between 0.75 and
 1. 24. The envelope of claim 15 wherein the angle of the shell is less than or equal to 40 degrees. 